Spacecraft to Skim Atmosphere of Saturn's Moon Titan

by SPACE.com Staff | June 18, 2010 04:32pm ET

Artist's concept of Cassini's flyby of Saturn's moon Titan. The spacecraft flies to within 547 miles (880 kilometers) of Titan's surface during its 71st flyby of Titan, known as "T70," the lowest in the entire mission.Credit: NASA/JPL-Caltech

NASA's Cassini spacecraft will get its best look at Saturn's
biggest moon Titan this weekend, when it takes the deepest dip yet into the
cloud-covered satellite's hazy atmosphere.

Cassini will fly 43 miles (70 km) lower into the atmosphere
of Titan than ever before when it swoops past the Saturnian moon in the early
morning of June 21 GMT (evening of June 20 Pacific Time). At its closest point,
the probe will be 547 miles (880 km) above Titan's
surface.

This is one of the most anticipated flybys of the Cassini
mission so far, C?sar Bertucci, one of the Cassini team scientists, wrote in a
blog post for NASA's Jet Propulsion Laboratory, located in Pasadena, Calif. The
flyby is the 71st Titan pass of the Cassini
mission since it arrived at Saturn in 2004.

It will be Cassini's first time flying below Titan's
ionosphere, the layer of electrons and other charged particles that make up the
upper part of the moon's atmosphere, Bertucci wrote.

By dipping this low, Cassini should be far enough away from Saturn's
magnetic field to be able to potentially detect magnetic signatures that
originate within Titan itself.

"We want to get as close to the surface with our
magnetometer as possible for a one-of-a-kind scan of the moon," Bertucci
wrote.

The goal, researchers said, is to find out if Titan has its
own magnetic field, which could help scientists understand more about the
moon's interior and geochemical evolution.

But first, Cassini mission scientists had to make sure it
was safe for their spacecraft to fly so deep into Titan's atmosphere.

The atmosphere of Titan applies torque, or rotational force,
on objects that fly through it in much the same way that the flow of air pushes
on a human hand sticking outside the window of a moving car. ?

Cassini's mission planners and the NASA Engineering and
Safety Center in Hampton, Va., have analyzed the torque applied by Titan's
atmosphere to confirm that the spacecraft can fly safely at its lowest-yet altitude
above the moon's surface.

By coincidence, the engineers discovered that the most
stable angle for Cassini to fly was the same as the angle required to point its
high-gain antenna to Earth.

So, by cocking the spacecraft a fraction of a degree, mission
managers should be able to track Cassini in real-time during its closest
approach. Thrusters will fire throughout the flyby in order to maintain this angle
and pointing automatically.

Cassini was slated to be decommissioned in September of this
year, but has received an extended
mission that now runs through 2017.